In a bowl, cream butter, oil and sugar. Beat in eggs and vanilla. Combine dry ingredients; add to the creamed mixture alternately with buttermilk. Mix well. Stir in zucchini. Pour into a greased 13-in. x 9-in. baking dish. Sprinkle with chocolate chips. Bake at 350° for 40-45 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack. Yield: 12-15 servings.